It is well known to make polyalphaolefins by reacting 1-decene with boron trifluoride and butanol. The oligomer product is a mixture of dimer, trimer, and higher molecular weight materials.
The market for the trimer and higher molecular weight materials is well established, both in military applications and in automotive and industrial uses that require a 4 centistokes (cSt) or greater kinematic viscosity. The dimer, which has a viscosity of about 2 cSt, was usually recycled to the reaction. That resulted in better economics but a somewhat poorer product performance. Because of the market demand for the trimer and higher molecular weight materials and lack of market demand for dimer production, most of the work in this area has involved minimizing the amount of dimers made.
The dimer is useful in heat transfer fluids, dielectric fluids, and lubricating fluids. Recently, it also has been found to be useful in drilling fluids. This involves replacing petroleum fractions, chiefly diesel oil, in oil-based drilling fluids with environmentally compatible polyalphaolefins. Oil-based drilling fluids are undesirable in off-shore petroleum exploration because those fluids produce an unwanted sheen on the water and are harmful to certain marine life. This new market for dimers has changed the economics of the industry. Now, there is an economic motivation to increase dimer yield, rather than minimize it.
U.S. Pat. Nos. 5,068,487; 5,171,905; and 5,171,918 disclose a process for producing predominately dimer and trimer. That process uses boron trifluoride in conjunction with alcohol alkoxylates EQU [RO(CHR'--CHR"O).sub.n --H].
Unfortunately, this process can create a highly viscous emulsion layer in the reactant and aqueous wash streams. These emulsions can cause operating difficulties, such as inhomogeneity in the reactor, process line plugging, poor product recovery, and lengthy phase separation times.
Other patents of interest are U.S. Pat. Nos. 3,769,363; 3,997,621; 4,218,330; 4,436,947; and 4,982,026.
U.S. Pat. No. 3,769,363 by Brennan discloses oligomerization of C.sub.6 -C.sub.12 normal .alpha.-olefins, such as 1-decene, with boron trifluoride and C.sub.5 carboxylic acid to improve trimer yields.
U.S. Pat. No. 3,997,621 by Brennan discloses oligomerization of C.sub.6 -C.sub.12 normal .alpha.-olefins using alcohols or water promoters in conjunction with small amounts of methyl and ethyl esters of a C.sub.2 -C.sub.5 mono carboxylic acid to improve trimer yields.
U.S. Pat. No. 4,218,330 by Shubkin discloses dimerization of a C.sub.12 -C.sub.18 monomer with a boron trifluoride-water complex and an excess of boron trifluoride. The product is distilled to remove the monomer and is hydrogenated for use as a crankcase lubricant. This product is mainly dimers, with minor amounts of trimers and higher oligomers. However, the monomer conversion is unacceptably low.
U.S. Pat. No. 4,436,947 by Morganson et al. discloses oligomerization of C.sub.6 -C.sub.20 olefins, such as 1-decene, with boron trifluoride and a mixture of an aliphatic alcohol, an aliphatic ketone, and a polyol. This product is predominately trimer.
U.S. Pat. No. 4,982,026 by Karn et al. discloses polymerization of lower alkene monomers (C.sub.2 -C.sub.6) with boron trifluoride and a strong acid, such as phosphoric acid, to produce a polymer having a molecular weight from 250 to 500 and having a high vinylidene content. Besides having a degree of oligomerization greater than two, the process requires subzero reaction temperatures, which are uneconomical.
U.S. Pat. Nos. 3,769,363; 3,997,621; 4,218,330; 4,436,947; 4,982,026 5,068,487; 5,171,905; and 5,171,918 are hereby incorporated by reference for all purposes.